Mobile telecommunications systems are normally statically configured with a parameter set defining the behavior of the system. The systems are based on standards which define radio bearers to carry traffic with different characteristics, e.g. speech, streaming video, or packet data. Standards such as the 3rd generation partnership project, 3GPP, standards define different so-called user equipment/radio resource control, UE/RRC, states. See, for example, 3GPP TS 25.331 V10.4.0 (2011-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control, RRC, Protocol specification (Release 10), which describes states such as CELL_DCH state, CELL_FACH state, CELL_PCH state, URA_PCH state, and the Idle state URA_PCH state. These names of these states are understood in view of the following channels/areas: Dedicated Channel, DCH, Forward Access Channel, FACH, Random Access Channel, RACH, and UTRAN registration area, URA_PCH.
For each wireless terminal in the connected mode, a node of the radio access network, such as a radio network controller, RNC, determines in which of these states the wireless terminal operates. Whichever of the UE/RRC states a wireless terminal currently is in has consequences which affect, e.g., the UE battery consumption and the resource consumption in the mobile network.
Packet data services have escalated, particularly with the introduction of wireless terminals in the form of devices such as smartphones, and with personal computers now widely participating in the mobile networks. Most of the packet traffic is based on the internet protocol, IP, e.g., internet services, and is normally treated as best effort traffic in the mobile network. Internet services are of many types and different characteristics, e.g. web browsing, chat, email, file sharing, and video streaming.
Within an IP flow there are typically times of activity and times of inactivity. Periods of activity will be separated by times of inactivity of different length. Within the IP flow, a burst may for example be defined by IP packets arriving with a an idle time between bursts, ITB, defined as the time between the last packet in one burst and the first packet of the next as illustrated in FIG. 1.
As mentioned above, a radio access network node such as the RNC keeps track of the UE/RRC state in which a wireless terminal is currently operating and also governs the transition of the wireless terminal between UE/RRC states. In other words, the RNC determines when a wireless terminal should transition from one UE/RRC state to another state. Parameters to govern the transition between UE/RRC states are normally timer based. FIG. 2 generally depicts that, when switching to a higher state, a wireless terminal may be required to transition from one UE/RRC state to another UE/RRC state upon expiration of a timer. The timer may be activated or initiated by some UE-related network activity, e.g. forwarding of an IP packet to/from the UE. The timer may expire due to some UE-related inactivity, e.g., no IP packet forwarded to/from the UE. Expiration of the timer may prompt the transition from one UE/RRC state to another UE/RRC state. Transfer to a state of higher activity is normally transmission-triggered, e.g., filling of a buffer.
High Speed Packet Access, HSPA, generally employs two mobile telephony protocols, High Speed Downlink Packet Access, HSDPA, and High Speed Uplink Packet Access, HSUPA, and as such extends and improves the performance of existing protocols. With HSPA it is now possible to provide mobile broadband since the peak bit rates reach up to 42 Mbps (3GPP R8) in downlink, and 11 Mbps (3GPP R8) in uplink. For 3GPP R9 the peak rates are doubled. Thus, HSPA may be seen as a complement and replacement to other broad band access such as Asymmetric Digital Subscriber Line, ADSL.
As mentioned above and illustrated in FIG. 3, the Idle, Cell_DCH, Cell_FACH, URA_PCH, and Cell_PCH are the five RRC protocol states. Data transfer between the UE and the network is only possible in Cell_FACH and Cell_DCH states. The Cell_DCH state is characterized by dedicated channels in both the uplink and the downlink. This corresponds to continuous transmission and reception and has the highest battery consumption. The Cell_FACH state does not use dedicated channels and thus allows lower battery consumption, at the expense of a lower uplink and downlink throughput. Thus, in addition to showing the RRC states, FIG. 3 also shows serves as an example state transition diagram. As understood from FIG. 3, the system typically does state transition due to amount of data in the RLC send buffers and due to the length of transmission inactivity.
In the example state transition diagram of FIG. 3, down-switch from CELL_DCH is based on inactivity timers. These may be set differently depending on traffic types, based on RNC load, with respect to UE power consumption or even specifically per user. A different approach is to use adaptive channel switching by predicting the time until the next data activity, i.e. to predict the IdleTime Between data bursts, ITB.
There is a difference in processor cost for an RNC associated with staying in the different states and to switch between the states. The cost is related to hardware resource consumption with respect to memory and implied processor load for a certain event, such a state channel switching event. The cost of residing in CELL_DCH may be approximately 10000 times that of staying in one of the lower states, e.g. CELL_FACH or URA_PCH. Hence from the RNC perspective, it is most efficient to avoid CELL_DCH except when needed due to requirements on data transmission rate. However, since there is also a processor cost associated with switching, down-switching is not economical unless the UE may stay in the lower state for a certain time (depending on the specific RNC load implication).
A different approach to use down-switch a timer is to use traffic adaptive channel switching, TACS. TACS involves predicting the time until the next data activity, i.e. to predict the ITB by using a prediction algorithm. If a short ITB is predicted, the user should stay on DCH while if a long ITB is predicted, the user should be down-switched to URA_PCH. The limit which discriminates between short and long ITBs is the ITB threshold, ITBTHR. Typically, this threshold is larger than the fixed down-switch timer which also leads to better user experience when TACS is used. Examples of adaptive channel switching are described, e.g., in U.S. provisional patent application 61/544,205, filed Oct. 6, 2011, entitled “DYNAMIC RADIO RESOURCE CONTROL STATE SWITCHING”.
The ITBTHR defined in the TACS approach is the time interval at which the cost of remaining in the first state is equal to the cost of switching to the second state and switching back to the first state. Although this definition may appear optimal, it suffers from being sub-optimal in reality since the ITB predictions are subject to errors. If ITBTHR is too small, there is no gain from doing a switch to the second state for ITBs which are just above ITBTHR, while if ITBTHR is too large, there is no gain from remaining in the first state for ITBs which are just below ITBTHR.